Adjustment of target signal-to-interference in outer loop power control for wireless communication systems

ABSTRACT

A method for outer loop power control which compensates for changing channel conditions. A target metric, preferably target signal-to-interference ratio (SIR), is adjusted with differing step up and step down levels to converge on a relatively low steady state level of step up and step down target metric adjustments. The initial target SIR remains fixed during an inner loop settling state, followed by incremental target SIR adjustments during a transient state, and smaller incremental target SIR adjustments in a steady state. Step sizes of the adjustments are preferably based on the target block error rate (BLER) and the number of errors detected within predetermined time intervals.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. application Ser. No.11/023,858 filed on Dec. 28, 2004, which claims priority from U.S.provisional application No. 60/551,872, filed Mar. 10, 2004, which isincorporated by reference as if fully set forth.

FIELD OF INVENTION

The invention generally relates to wireless communication systems. Inparticular, the invention relates to power control in such systems.

BACKGROUND

Wireless telecommunication systems are well known in the art. In orderto provide global connectivity for wireless systems, standards have beendeveloped and are being implemented. One current standard in widespreaduse is known as Global System for Mobile Telecommunications (GSM). Thisis considered as a so-called Second Generation mobile radio systemstandard (2G) and was followed by its revision (2.5G). GPRS and EDGE areexamples of 2.5G technologies that offer relatively high speed dataservice on top of (2G) GSM networks. Each one of these standards soughtto improve upon the prior standard with additional features andenhancements. In January 1998, the European Telecommunications StandardInstitute—Special Mobile Group (ETSI SMG) agreed on a radio accessscheme for Third Generation Radio Systems called Universal MobileTelecommunications Systems (UMTS). To further implement the UMTSstandard, the Third Generation Partnership Project (3GPP) was formed inDecember 1998. 3GPP continues to work on a common third generationalmobile radio standard.

A typical UMTS system architecture in accordance with current 3GPPspecifications is depicted in FIG. 1. The UMTS network architectureincludes a Core Network (CN) interconnected with a UMTS TerrestrialRadio Access Network (UTRAN) via an interface known as Iu which isdefined in detail in the current publicly available 3GPP specificationdocuments. The UTRAN is configured to provide wireless telecommunicationservices to users through wireless transmit receive units (WTRUs), knownas User Equipments (UEs) in 3GPP, via a radio interface known as Uu. TheUTRAN has one or more Radio Network Controllers (RNCs) and basestations, known as Node Bs in 3GPP, which collectively provide for thegeographic coverage for wireless communications with UEs. One or moreNode Bs are connected to each RNC via an interface known as Iub in 3GPP.The UTRAN may have several groups of Node Bs connected to differentRNCs; two are shown in the example depicted in FIG. 1. Where more thanone RNC is provided in a UTRAN, inter-RNC communication is performed viaan Iur interface.

Communications external to the network components are performed by theNode Bs on a user level via the Uu interface and the CN on a networklevel via various CN connections to external systems.

In general, the primary function of base stations, such as Node Bs, isto provide a radio connection between the base stations' network and theWTRUs. Typically a base station emits common channel signals allowingnon-connected WTRUs to become synchronized with the base station'stiming. In 3GPP, a Node B performs the physical radio connection withthe UEs. The Node B receives signals over the Iub interface from the RNCthat control the radio signals transmitted by the Node B over the Uuinterface.

A CN is responsible for routing information to its correct destination.For example, the CN may route voice traffic from a UE that is receivedby the UMTS via one of the Node Bs to a public switched telephonenetwork (PSTN) or packet data destined for the Internet. In 3GPP, the CNhas six major components: 1) a serving General Packet Radio Service(GPRS) support node; 2) a gateway GPRS support node; 3) a bordergateway; 4) a visitor location register; 5) a mobile services switchingcenter; and 6) a gateway mobile services switching center. The servingGPRS support node provides access to packet switched domains, such asthe Internet. The gateway GPRS support node is a gateway node forconnections to other networks. All data traffic going to otheroperator's networks or the Internet goes through the gateway GPRSsupport node. The border gateway acts as a firewall to prevent attacksby intruders outside the network on subscribers within the networkrealm. The visitor location register is a current serving networks‘copy’ of subscriber data needed to provide services. This informationinitially comes from a database which administers mobile subscribers.The mobile services switching center is in charge of ‘circuit switched’connections from UMTS terminals to the network. The gateway mobileservices switching center implements routing functions required based oncurrent location of subscribers. The gateway mobile services switchingcenter also receives and administers connection requests fromsubscribers from external networks.

The RNCs generally control internal functions of the UTRAN. The RNCsalso provides intermediary services for communications having a localcomponent via a Uu interface connection with a Node B and an externalservice component via a connection between the CN and an externalsystem, for example overseas calls made from a cell phone in a domesticUMTS.

Typically a RNC oversees multiple base stations, manages radio resourceswithin the geographic area of wireless radio service coverage servicedby the Node Bs and controls the physical radio resources for the Uuinterface. In 3GPP, the Iu interface of an RNC provides two connectionsto the CN: one to a packet switched domain and the other to a circuitswitched domain. Other important functions of the RNCs includeconfidentiality and integrity protection.

In many wireless communication systems, adaptive transmission powercontrol algorithms are used. In such systems, many communications mayshare the same radio frequency spectrum. When receiving a specificcommunication, all the other communications using the same spectrumcause interference to the specific communication. As a result,increasing the transmission power level of one communication degradesthe signal quality of all other communications within that spectrum.However, reducing the transmission power level too far results inundesirable received signal quality, such as measured by signal tointerference ratios (SIRs) at the receivers.

Various methods of power control for wireless communication systems arewell known in the art. Examples of open and closed loop power controltransmitter systems for wireless communication systems are illustratedin FIGS. 2 and 3, respectively. The purpose of such systems is torapidly vary transmitter power in the presence of a fading propagationchannel and time-varying interference to minimize transmitter powerwhile insuring that data is received at the remote end with acceptablequality.

In communication systems such as Third Generation Partnership Project(3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD)systems, multiple shared and dedicated channels of variable rate dataare combined for transmission. Background specification data for suchsystems are found at 3GPP TS 25.223 v3.3.0, 3GPP TS 25.222 v3.2.0, 3GPPTS 25.224 v3.6 and Volume 3 specifications of Air-Interface for 3GMultiple System Version 1.0, Revision 1.0 by the Association of RadioIndustries Businesses (ARIB). A fast method and system of power controladaptation for data rate changes resulting in more optimal performanceis taught in International Publication Number WO 02/09311 A2, published31 Jan. 2002 and corresponding U.S. patent application Ser. No.09/904,001, filed Jul. 12, 2001 owned by the assignee of the presentinvention.

In 3GPP W-CDMA systems, power control is used as a link adaptationmethod. Dynamic power control is applied for dedicated physical channels(DPCH), such that the transmit power of the DPCHs is adjusted to achievea quality of service (QoS) with a minimum transmit power level, thuslimiting the interference level within the system.

One approach is to divide transmission power control into separateprocesses, referred to as outer loop power control (OLPC) and inner looppower control (ILPC). The power control system is generally referred toas either open or closed dependent upon whether the inner loop is openor closed. The outer loops of both types of systems as illustrated inthe examples depicted in FIGS. 2 and 3 are closed loops. The inner loopin the open loop type of system illustrated in FIG. 2 is an open loop.

In outer loop power control, the power level of a specific transmitteris based on a target SIR value. As a receiver receives thetransmissions, the quality of the received signal is measured. Thetransmitted information is sent in units of transport blocks (TBs), andthe received signal quality can be monitored on a block error rate(BLER) basis. The BLER is estimated by the receiver, typically by acyclic redundancy check (CRC) of the data. This estimated BLER iscompared to a target quality requirement, such a target BLER,representative of QoS requirements for the various types of dataservices on the channel. Based on the measured received signal quality,a target SIR adjustment control signal is sent to the transmitter. Thetransmitter adjusts the target SIR in response to these adjustmentrequests.

In third generation partnership program (3GPP) wideband code divisionmultiple access (W-CDMA) systems utilizing time division duplex (TDD)mode, the UTRAN (SRNC-RRC) sets the initial target SIR to the WTRU atthe call/session establishment and then subsequently continuouslyadjusts the target SIR of the WTRU during the life term of the call asdictated by the observation of the uplink (UL) BLER measurement.

In inner loop power control, the receiver compares a measurement of thereceived signal quality, such as SIR, to a threshold value (i.e., thetarget SIR). If the SIR exceeds the threshold, a transmit power command(TPC) to decrease the power level is sent. If the SIR is below thethreshold, a TPC to increase the power level is sent. Typically, the TPCis multiplexed with data in a dedicated channel to the transmitter. Inresponse to received TPC, the transmitter changes its transmission powerlevel.

Conventionally, the outer loop power control algorithm in a 3GPP systemsets an initial target SIR for each coded composite transport channel(CCTrCH) based on the required target BLER, using a fixed mappingbetween BLER and SIR, assuming a particular “most plausible” channelcondition. A CCTrCH is commonly employed for transmitting variousservices on a physical wireless channel by multiplexing severaltransport channels (TrCHs), each service on its own TrCH. In order tomonitor the BLER level on a CCTrCH basis, a reference transport channel(RTrCH) may be selected among the transport channels multiplexed on theconsidered CCTrCH. For example, a TrCH-1 may be selected for RTrCH as itmay be regarded as a mid-point of all channel conditions on the CCTrCH,including an additive white Gaussian noise (AWGN) channel. For example,FIG. 4 shows typical downlink simulation results of Wideband CodeDivision Multiple Access Time Division Duplex (WCDMA TDD) for variouschannel conditions specified in 3GPP using a zero-forcing multi-userdetector. Results are shown for various propagation conditions. A staticchannel is represented by curve AWGN, while curves for Cases 1 through 3represent fading channels with different multipath profiles. At arequired BLER of 0.01 for the Case 1 fading channel, a predeterminedtransmission power can be determined from the target SIR ofapproximately 4.5 dB. Note that this is more than 5 dB over the targetSIR for the Case 2 fading channel and more than 12 dB over the targetSIR for AWGN, illustrating the large span of target SIR values dependingon the assumed propagation condition.

Based on the above example, the mismatch between the required BLER andthe mapped target SIR varies depending on the actual channel conditionand it is large especially at very low BLERs. When the WTRU converts thetarget BLER to an initial target SIR, there may be an error caused bythis channel condition mismatch, since the target SIR required for atarget BLER varies with channel conditions. As a result, the iterativeprocess for target SIR determination has an initial differential thatmust be overcome by convergence to the required target, compounded byallowing the CRC process to occur, which altogether creates anundesirable delay for target SIR convergence.

The entire power control algorithm may suffer degraded performance as aresult of the delay. The delay is denoted in terms of the transmissionrate unit, a transmission time interval (TTI). The smallest interval isone frame of data, typically defined as 10 ms for a 3GPP communicationsystem. In a 3GPP system, TTIs are in lengths of 10, 20, 40, or 80 ms.

There are four main error sources in transmission power control: 1)systematic error; 2) random measurement error; 3) CCTrCH processingerror; and 4) channel error. The systematic error and the randommeasurement error are corrected reasonably by the inner loop powercontrol monitoring the SIR measurements. The CCTrCH processing error iscorrected by either the outer loop power control or the inner loop powercontrol by using relative SIR measurements among the codes. The channelerror is related to unknown time varying channel conditions.

Accordingly, there is a need for outer loop power control thatdetermines the actual channel conditions so that a proper value for thetarget SIR is used.

SUMMARY

An apparatus and method of transmission power control is provided for awireless transmit receive unit (WTRU) that transmits data signals in aforward channel in selectively sized block allocations where the WTRU isconfigured to make forward channel power adjustments as a function oftarget metrics computed based on the data signals as received over theforward channel. A series of data signal block allocations is receivedspaced apart in time from the WTRU on the forward channel. Targetmetrics for the WTRU's forward channel power adjustments are computedbased on the detection of predetermined error conditions in the signalsreceived on the forward channel, including setting an initial targetmetric value and storing a last target metric computed for each blockallocation of data. After a preliminary period at the initial value, thetarget metric is changed by a step up or a step down amount at timeintervals of a predetermined length whereby the target metric isincreased by the step up amount if a predetermined error condition hasbeen detected in an immediately preceding time interval or is decreasedby the step down amount if the predetermined error condition has notbeen detected the immediately preceding time interval. Setting the stepdown amount at an initial transient state level is preferably based onthe required quality of signal or block error ratio (BLER), such thatthe initial step down amount is set at a level at least as great as apredetermined step down amount for a steady state steady state level.The step down amount has a scaling factor inversely proportional to thenumber of detected errors during the time interval being processed. If apredetermined error condition has been detected in an immediatelypreceding time interval, the step down amount is reduced by a selectedamount to a lower level until the step down amount is reduced to thepredetermined step down amount for the steady state steady state level.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 shows an overview of a system architecture of a conventional UMTSnetwork.

FIG. 2 is a schematic diagram of a conventional open loop power controlsystem for a wireless communication system which implements outer looppower control via a target SIR metric.

FIG. 3 is a schematic diagram of a conventional closed loop powercontrol system for a wireless communication system which implementsouter loop power control via a target SIR metric.

FIG. 4 is a graphical representation of required BLER versus target SIRaccording to a simulation of a Wideband Code Division Multiple AccessTime Division Duplex (W-CDMA TDD) receiver for various channelconditions using a multi-user detector.

FIG. 5 illustrates a plot of target SIR adjustments according with ajump algorithm as applicable to downlink OLPC.

FIG. 6 illustrates a plot of target SIR adjustments of an exemplary WTRUdownlink OLPC in accordance with the teachings of the present invention.

FIG. 7 illustrates a plot of target SIR adjustments of an exemplary WTRUdownlink OLPC with a compressed transient state in accordance with theteachings of the present invention.

FIGS. 8A-8C illustrate a method flowchart of an exemplary downlink OLPCalgorithm in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is described with reference to the drawing figureswherein like numerals represent like elements throughout. The terms basestation, wireless transmit/receive unit (WTRU) and mobile unit are usedin their general sense. The term base station as used herein includes,but is not limited to, a base station, Node-B, site controller, accesspoint, or other interfacing device in a wireless environment thatprovides WTRUs with wireless access to a network with which the basestation is associated.

The term WTRU as used herein includes, but is not limited to, userequipment (UE), mobile station, fixed or mobile subscriber unit, pager,or any other type of device capable of operating in a wirelessenvironment. WTRUs include personal communication devices, such asphones, video phones, and Internet ready phones that have networkconnections. In addition, WTRUs include portable personal computingdevices, such as PDAs and notebook computers with wireless modems thathave similar network capabilities. WTRUs that are portable or canotherwise change location are referred to as mobile units.

Although the embodiments are described in conjunction with a thirdgeneration partnership program (3GPP) wideband code division multipleaccess (W-CDMA) system utilizing the time division duplex mode, theembodiments are applicable to any hybrid code division multiple access(CDMA)/time division multiple access (TDMA) communication system.Additionally, the embodiments are applicable to CDMA systems, ingeneral, such as the proposed frequency division duplex (FDD) mode of3GPP W-CDMA.

Conventional power control methods for wireless systems such as 3GPPutilize so-called inner and outer loops. The power control system isreferred to as either open or closed dependent upon whether the innerloop is open or closed. The outer loops of both types of systems areclosed loops.

Pertinent portions of an open loop power control system having a“transmitting” communication station 10 and a “receiving” communicationstation 30 are shown in FIG. 2. Both stations 10, 30 are transceivers.Typically one is a base station, called a Node B in 3GPP, and the othera type of WTRU, called a user equipment UE in 3GPP. For clarity, onlyselected components are illustrated and the invention is described interms of a preferred 3GPP system, but the invention has application towireless communication systems in general, even such systems thatperform ad hoc networking where WTRUs communicate between themselves.Power control is important to maintain quality signaling for multipleusers without causing excessive interference.

The transmitting station 10 includes a transmitter 11 having a data line12 which transports a user data signal for transmission. The user datasignal is provided with a desired power level which is adjusted byapplying a transmit power adjustment from an output 13 of a processor 15to adjust the transmission power level. The user data is transmittedfrom an antenna system 14 of the transmitter 11.

A wireless radio signal 20 containing the transmitted data is receivedby the receiving station 30 via a receiving antenna system 31. Thereceiving antenna system will also receive interfering radio signals 21which impact on the quality of the received data. The receiving station30 includes an interference power measuring device 32 to which thereceived signal is input which device 32 outputs measured interferencepower data. The receiving station 30 also includes a data qualitymeasuring device 34 into which the received signal is also input whichdevice 34 produces a data quality signal. The data quality measuringdevice 34 is coupled with a processing device 36 which receives thesignal quality data and computes target signal to interference ratio(SIR) data based upon a user defined quality standard parameter receivedthrough an input 37.

The receiving station 30 also includes a transmitter 38 which is coupledwith the interference power measuring device 32 and the target SIRgenerating processor 36. The receiving station's transmitter 38 alsoincludes inputs 40, 41, 42 for user data, a reference signal, andreference signal transmit power data, respectively. The receivingstation 30 transmits its user data and the control related data andreferences signal via an associated antenna system 39.

The transmitting station 10 includes a receiver 16 and an associatedreceiving antenna system 17. The transmitting station's receiver 16receives the radio signal transmitted from the receiving station 30which includes the receiving station's user data 44 and the controlsignal and data 45 generated by the receiving station 30.

The transmitting station's transmitter's processor 15 is associated withthe transmitting station's receiver 16 in order to compute a transmitpower adjustment. The transmitter 11 also includes a device 18 formeasuring received reference signal power which device 18 is associatedwith path loss computing circuitry 19.

In order to compute the transmit power adjustment, the processor 15receives data from a target SIR data input 22 which carries the targetSIR data generated by the receiver station's target SIR generatingprocessor 36, an interference power data input 23 which carries theinterference data generated by the receiving station's interferencepower measuring device 32, and a path loss data input 24 which carries apath loss signal that is the output of the path loss computing circuitry19. The path loss signal is generated by the path loss computingcircuitry 19 from data received via a reference signal transmit powerdata input 25 which carries the reference signal transmit power dataoriginating from the receiving station 30 and a measured referencesignal power input 26 which carries the output of the reference signalpower measuring device 18 of the transmitter 11. The reference signalmeasuring device 18 is coupled with the transmitting station's receiver16 to measure the power of the reference signal as received from thereceiving station's transmitter 38. The path loss computing circuitry 19preferably determines the path loss based upon the difference betweenthe known reference power signal strength conveyed by input 25 and themeasured received power strength conveyed by input 26.

Interference power data, reference signal power data and target SIRvalues are signaled to the transmitting station 10 at a ratesignificantly lower than the time-varying rate of the propagationchannel and interference. The “inner” loop is the portion of the systemwhich relies on the measured interface. The system is considered “openloop” because there is no feedback to the algorithm at a rate comparableto the time-varying rate of the propagation channel and interferenceindicating how good the estimates of minimum required transmitter powerare. If required transmit power level changes rapidly, the system cannotrespond accordingly to change the power adjustment in a timely manner.

With respect to the outer loop of the open loop power control system ofFIG. 2, at the remote receiver station 30, the quality of the receiveddata is evaluated via the measuring device 34. Typical metrics fordigital data quality are bit error rate and block error rate.Computation of these metrics requires data accumulated over periods oftime significantly longer than the period of the time-varyingpropagation channel and interference. For any given metric, there existsa theoretical relationship between the metric and received SIR. Whenenough data has been accumulated in the remote receiver to evaluate themetric, it is computed and compared with the desired metric(representing a desired quality of service) in processor 36 and anupdated target SIR is then output. The updated target SIR is that value(in theory) which applied in the transmitter inner loop would cause themeasured metric to converge to the desired value. Finally, the updatedtarget SIR is passed, via the receiving station transmitter 38 and thetransmitting station receiver 16, to the transmitter 11 for use in itsinner loop. The update rate of target SIR is bounded by the timerequired to accumulate the quality statistic and practical limits on thesignaling rate to the power-controlled transmitter.

With reference to FIG. 3, a communication system having a transmittingstation 50 and a receiving station 70 which employs a closed loop powercontrol system is illustrated.

The transmitting station 50 includes a transmitter 51 having a data line52 which transports a user data signal for transmission. The user datasignal is provided with a desired power level which is adjusted byapplying a transmit power adjustment from an output 53 of a processor 55to adjust the power level. The user data is transmitted via an antennasystem 54 of the transmitter 51.

A wireless radio signal 60 containing the transmitted data is receivedby the receiving station 70 via a receiving antenna system 71. Thereceiving antenna system will also receive interfering radio signals 61which impact on the quality of the received data. The receiving station70 includes an interference power measuring device 72 to which thereceived signal is input which device 72 outputs measured SIR data. Thereceiving station 70 also includes a data quality measuring device 73into which the received signal is also input which device 73 produces adata quality signal. The data quality measuring device 73 is coupledwith a processor 74 which receives the signal quality data and computestarget signal to interference ratio (SIR) data based upon a user definedquality standard parameter received through an input 75.

A combiner 76, preferably a substracter, compares the measured SIR datafrom the device 72 with the computed target SIR data from the processor74, preferably by subtracting, to output an SIR error signal. The SIRerror signal from the combiner 76 is input to processing circuitry 77which generates step up/down commands based thereon.

The receiving station 70 also includes a transmitter 78 which is coupledwith the processing circuitry 77. The receiving station's transmitter 78also includes an input 80 for user data. The receiving station 70transmits its user data and the control related data via an associateantenna system 79.

The transmitting station 50 includes a receiver 56 and an associatedreceiving antenna system 57. The transmitting station's receiver 56receives the radio signal transmitted from the receiving station 70which includes the receiving station's user data 84 and the control data85 generated by the receiving station.

The transmitting station's transmitter's processor 55 has an input 58associated with the transmitting station's receiver 16. The processor 55receives the up/down command signal through input 58 and computes thetransmit power adjustments based thereon.

With respect to the inner loop of the closed loop power control system,the transmitting station's transmitter 51 sets its power based uponhigh-rate step up and step down commands generated by the remotereceiving station 70. At the remote receiving station 70, the SIR of thereceived data is measured by the measuring device 72 and compared with atarget SIR value generated by the processor 74 via combiner 76. Thetarget SIR is that value (in theory) which, given that the data isreceived with that value, results in a desired quality of service. Ifthe measured received SIR is less than the target SIR, a step downcommand is issued by the processing circuitry 77, via the receivingstation's transmitter 78 and the transmitting station's receiver 56, tothe transmitter 51, otherwise a step up command is issued. The powercontrol system is considered closed-loop because of the high-ratefeedback of the step up and step down commands which can react in realtime to the time-varying propagation channel and interference. Ifrequired transmit power level changes due to time varying interferenceand propagation, it quickly responds and adjusts transmit poweraccordingly.

With respect to the outer loop of the closed loop power control system,the quality of the received data is evaluated in the receiving station70 by the measuring device 73. Typical metrics for digital data qualityare bit error rate and block error rate. Computation of these metricsrequires data accumulated over periods of time significantly longer thanthe period of the time-varying propagation channel and interference. Forany given metric, there exists a theoretical relationship between themetric and received SIR. When enough data has been accumulated in theremote receiver to evaluate the metric, it is computed and compared withthe desired metric (representing a desired quality of service) by theprocessor 74 and an updated target SIR is then output. The updatedtarget SIR is that value (in theory) which applied in the receiveralgorithm would cause the measured metric to converge to the desiredvalue. The updated target SIR is then used in the inner loop todetermine the direction of the step up/down commands sent to thetransmitting station's power scale generating processor 55 to controlthe power of the transmitter 51.

For outer loop power control, irrespective of its implementation ineither an open loop system as illustrated in FIG. 2 or a closed loopsystem as illustrated in FIG. 3, an initial target metric, such astarget SIR, is set that is then recomputed based on the outer loopfeedback occurring during a wireless communication. Conventionally, theadjustment the target metric is performed using a fixed step methodwhere set increments of step up and step down are employed to convergeon a desired target.

After an initial target SIR is set, the down link outer loop powercontrol process utilizes a “jump” algorithm that adjusts a target SIRbased on the result of CRC of the data. FIG. 5 graphically illustratesthe use of a generic jump algorithm. Each step up and step down intarget SIR is a relatively fixed step size adjustment, once at thebeginning of each TTI. A CRC is preferably performed at each TTI, andstep down adjustments are made for every CRC having no error, while upona CRC error detection, a step up adjustment is made.

In a preferred embodiment of the present invention, the basic jumpalgorithm is represented by the following. If the CRC check of thek^(th) block does not detect an error, thentarget_SIR(k)=target_SIR(k−1)−SD (dB),  Equation 1else, if a CRC error occurs, thentarget_SIR(k)=target_SIR(k−1)+SU (dB)  Equation 2where step down SD and step up SU are calculated by the followingequations:SD=SS*target_(—) BLER  Equation 3SU=SS−SD  Equation 4where SS is the step size for the adjustment to target SIR, which isfurther discussed below in conjunction with the preferred step sizevariations used in accordance to the teachings of the present invention.

There are generally three states for down link outer loop power control:a preliminary inner loop settling state, a transient state, and a steadystate. An example of the adjustments to target SIR during the differentdown link outer loop power control states in accordance with theinvention is illustrated in FIG. 6. A method and system for adjustingdownlink outer loop power to control target SIR is taught in U.S. patentapplication Ser. No. 10/659,673, filed Sep. 10, 2003, owned by theassignee of the present invention.

As shown in FIG. 6, target SIR is preferably maintained constantthroughout the inner loop settling state. In the inner loop settlingstate, the inner loop TPC algorithm corrects the initial systemsystematic error and the random measurement error without changing theinitial target SIR.

In the transient state, the outer loop power control algorithm attemptsto correct the initial target SIR error caused by the channel conditionmismatch. Initially, the jump algorithm in the transient statepreferably uses a large step down size to decrease the target SIRrapidly, i.e., it forces a CRC error to occur. In the steady state, theouter loop power control algorithm attempts to maintain a target SIR byutilizing a relatively small step down size. One aspect invention ofthis exemplary WTRU downlink OLPC is to transition a relatively largestep size initially used in the transient state to a smaller step sizeutilized in the steady state. Another aspect of this example is toincrease the step size in the steady state where no CRC error occurswithin a predetermined period.

In the transient state, a large initial step size SS_(TS) can becalculated, for example, based upon the target BLER as follows:SS_(TS)=2log₁₀(1/target_(—) BLER) (dB)  Equation 5For example, where target_BLER=10 ⁻², then SS_(TS)=4 dB. Then, throughthe application of equations 3 and 4 above, the initial step down andstep up values for the transient state SD_(T), SU_(T) areSD_(T)=(4×10⁻²)=0.04 dB and SU_(T)=(4−0.04)=3.96 dB.

The occurrence of CRC errors is used to trigger reduction in the stepsize until the transient state step size converges to the step size ofthe steady state SS_(SS). For this example, the steady state SS_(SS) ispreferably calculated as follows:SS _(SS)=0.25[log₁₀(1/target_(—) BLER) (dB)  Equation 6Preferably, when a CRC error occurs during a TTI in the transient state,the step size is preferably reduced by ½. The reduced step size is thenapplied to the jump algorithm. The procedure iterates until the new stepsize converges to the step size of the steady state. For the aboveexample, convergence occurs after three iterations sinceSS_(TS)=2³*SS_(SS). Accordingly, for each TTI having a CRC error duringthe transient state, the next step size is preferably reduced from theinitial step size SS_(TS) by ½^(n), where n is the number of TTIs sincethe start of transient state that contained at least one CRC error,until the new step size converges to the step size of the steady state.When convergence occurs, the steady state is entered and no furtherreduction of step size occurs.

FIG. 6 provides a graphic illustration of the above example in practice.At a first CRC error at point A, the target SIR is increased byapproximately one half of a transient state step up according toEquation 4 (i.e., target SIR≈SU_(T)/2). The CRC error also causes anadjustment in the step down size; subsequent transport blocks receivedwithout CRC error result in a one-half decrease in target SIR accordingto Equation 3. When the next CRC error occurs, the step up size isreduced to one-fourth the original step up size (SU_(T)/4), target SIRis approximately increased by that amount, and the step down size isadjusted to SD_(T)/4. This algorithm continues until the adjusted stepup size SU_(T) equals the steady state step up size SU_(S), which in theexample shown in both FIGS. 6 and 7, is equal to SU_(T)/8. At thispoint, steady state is entered. The step up and step down sizes arefixed at SU_(S) and SD_(S), respectively. While the proportion value ofpredetermined step sizes for transient state and steady state ispreferably 2³, as shown in Equations 3 and 4 and described in the aboveexamples, this proportion value can be adjusted to suit channelconditions within the scope of the present invention.

The convergence to the steady state can be quite rapid where CRC errorsare successively detected upon entering the transient state. FIG. 7illustrates this for the above example where several transport blocksare received with CRC error immediately after the transient state isentered, resulting in successive decreases by a transient state step upSU_(T) in the target SIR. As shown in FIG. 7, the initial CRC resultindicates an error at point A, which results in a step up in target SIRby approximately SU_(T)/2, and setting of the step down size toSD_(T)/2. FIG. 7 also illustrates the possibility where the first CRCresult after a step up indicates an error. In such case as shown atpoint B, the target SIR is increased again, but by approximatelyone-fourth the original step size (i.e., target SIR≈SU_(T)/4). Tocontinue this worst case scenario, a CRC error occurs again at the thirdTTI in the transient state. The next target SIR step up adjustmentbecomes approximately one-eighth the original value (i.e., targetSIR≈SU_(T)/8). Because this step up is equal to the predetermined steadystate step up SU_(S), the transient state ends at this point, and thesteady state commences. The target SIR is consequently increased bySU_(S)=SU_(T)/8, and the step down size is set to SD_(S)=SD_(T)/8.Generally, any CRC error, regardless of when it occurs, will initiate astep up in target SIR by an amount that is half of the previous step up.

After the steady state is entered the step up and step down sizes aregenerally maintained at SU_(S) and SD_(S), respectively. Typically,where there is little change in the communication metrics, the steadystate algorithm produces a series of successive step up and step downcommands in a regular pattern (not shown) as is the case with theconventional jump algorithm. However, where the communication is subjectto a rapid change in operating conditions due to changes in interferenceor other factors, application of the steady state algorithm can be lessefficient. Accordingly, the steady state is varied from time to time tomeet rapidly changing conditions.

During the steady state, when a predetermined observation period ispassed with no CRC error occurrence, the step down size is preferablyautomatically increased. For example, as illustrated in FIGS. 6 and 7,after the passage of eight TTIs without a CRC error, the step down sizeis temporarily doubled so that the eighth and following consecutive stepdowns are twice the SD_(S) amount.

It is preferable that the observation period be relatively long as it isassumed that the target SIR is close to convergence. Preferably, theobservation period is set to 5/(target BLER) consecutive TTIs. Forexample, if the target BLER is 0.01, then the observation period wouldequal 500 consecutive TTIs. The step down value 2SD_(S) remains fixeduntil a CRC error occurs, when it is then returned to SD_(S). Thisimproves the convergence time when a sudden improvement in channelconditions occurs, giving rise to an excessive measured SIR compared tothe desired target SIR. The steady state continues for the life of theCCTrCH communication with this type of adjustment preferably being madewhenever there is no CRC error in a time increment equal to theobservation period.

Alternatively, when a predetermined observation period is passed with noCRC error occurrence, the process can revert back to the transient stateto reduce convergence time, and then proceed to steady state once thetarget SIR converges in the same manner as before. In such case, for theabove example, the step down value would switch from SD_(S) to SD_(TS)as defined above and then be incrementally reduced to the steady statevalue is CRC errors are detected.

The outer loop algorithm described above is preferably implemented in aprocessor that computes the target SIR such as processor 36 of the openloop system illustrated in FIG. 2 and processor 74 of the closed loopsystem illustrated in FIG. 3. The implementation of the algorithmdetermines whether any CRC errors occur in a new TTI, adjusts the stepup and step down sizes appropriately, then applies the step adjustmentsbased on the individual CRC results.

For a 3GPP system, in both the transient and steady states, if the RTrCHis reselected (e.g., for variable bit rate services) and the target BLERof that new RTrCH is different from the old, then the SIR step sizes arerecalculated based on the new target BLER. In steady state, theobservation period is also updated, and the current count of blockswithout error is reset to zero. In transient state, in addition torecalculating the step sizes, an additional adjustment is made toaccount for the convergence that may already have occurred in thisstate. In other words, the initial step up SU or step down SD values arenot applied, but rather the current adjustment for detected CRC errorsis applied. As before, the fractional step up or step down size iscalculated with a factor ½^(n), where n is the number of TTIs since thestart of transient state that contained at least one CRC error. Forexample, if the current step down size before RTrCH reselection isSD_(Told)/4, then the step down size immediately after RTrCH reselectionmust be set to SD_(Tnew)/4 and the step up size must be set toSU_(Tnew)/4.

In FIGS. 8A-8C, a flowchart for implementing the preferred algorithm fordownlink outer loop power control in a 3GPP system is provided. In FIG.8A, stage 300 represents preferred procedures during the inner loopsettling state. In step 302, the parameters for inner loop settlingtime, transient state step size SS_(TS), steady state step size SS_(SS),and TTI count are initialized. The settling state starts upon activationof the downlink physical channel(s). The settling state lasts for afinite period of time, based on performance requirement. In oneembodiment of the invention, inner loop settling time is set to 100 ms,for a time division duplex (TDD) communication. In another embodiment ofthe invention, for frequency division duplex (FDD), inner loop settlingtime is set to 10 or 30 ms depending on the frequency of operation ofpower control. During the settling state period, no adjustments are madeto the initial target signal-to-interference ratio (SIR). The measuredSIR converges toward the initial target SIR value as a result of innerloop power control which sends commands to the Node B requesting it toadjust its transmit power up or down based on the difference between themeasured SIR(s) and the target SIR. The values for transient state stepsize SS_(TS) and steady state step size SS_(SS) are initializedaccording to Equations 5 and 6 above, respectively. The value for theTTI count is set to zero (0).

In step 304, a comparison is made between the product (TTI count * TTIlength) and a predetermined inner loop settling time. If the product isgreater than the inner loop settling time, then the settling state iscomplete, and the power control algorithm proceeds to the transientstate. If not, the TTI count is incremented by one (1) in step 306, andthe settling state returns to step 304 for another comparison. Thus, thealgorithm stage 300 assures that enough TTIs have elapsed to allow theinner loop power control to correct initial systematic error and randommeasurement error.

In FIG. 8B, stage 307 represents preferred procedures for downlink outerloop power control which occur during the transient state. Step 308 isinitiated by the affirmative decision of step 304 from the FIG. 8Aportion of the flow chart. In step 308, the transient state parametersare initialized. The step size is preferably set to SS_(TS) according toEquation 5, the transient state step down is the step size factored bythe target BLER value (i.e., SD_(T)=target_BLER*SS_(TS)), and thetransient state step up SU_(T) is the difference between the step sizeSS_(TS) and the step down value SD_(T) (i.e., SU_(T)=SS_(TS)−SD_(T)).

In Step 310, a comparison is made between the step size SS_(TS) and thesteady state step size SS_(SS). The initial value for SS_(TS) isaccording to Equation 5 as determined in step 302. In step 310, adecision is made as to whether step size SS_(TS) is greater than steadystate step size SS_(SS). If not, the transient state is complete and thealgorithm proceeds to step 321 of FIG. 8C. If so, the method proceeds tostep 312 where it is checked whether N_(E) number of TTI CRC errors areat least one in number. If not, the method proceeds to step 317 wherethe target SIR is decreased according to the following equation:target_SIR=current_target_SIR−SD_(T)  Equation 7In step 317, target SIR is set to at least a minimum valueminimum_DL_SIR. That is, if target SIR is less than a predeterminedvalue minimum_DL_SIR, the target SIR is then set equal to that minimumvalue. With step 317 complete, the process returns to step 310 with thenewly decreased target SIR.

Returning to step 312, if at least one CRC error has been detected forthe current TTI, the transient state step size SS_(TS) is set to half ofthe current value of SS_(TS) (step 314). Again, the step size SS_(TS) iscompared to the steady state step size SS_(SS) (step 315). If the stepsize SS_(TS) is not greater than the steady state step size SS_(SS),then the transient state is complete and the algorithm proceeds to step321 of FIG. 8C. Otherwise, the method proceeds to step 316, where stepup SU_(T) and step down SD_(T) values are adjusted to the new step sizeSS_(TS) reduced in step 314, and the target SIR is increased accordingto the following equation:target_(—) SIR=current_target_(—) SIR+SU _(T)  Equation 8The new target SIR value is checked for being no greater than apredetermined maximum value Maximum_DL_SIR. If the new target SIR isfound to be greater than this maximum value, the new target SIR is resetto maximum value Maximum_DL_SIR. The transient state continues byreturning to step 310 and repeating the cycle until the transient statestep size becomes less than or equal to the steady state step size insteps 310 or 315.

Returning to step 315, if the step size SS_(TS) is greater than thesteady state step size, then the target SIR is increased by the value ofSU_(T) (step 316). If this adjustment to target SIR surpasses thepredetermined maximum value Maximum_DL_SIR, then target SIR is set toMaximum_DL_SIR before returning to step 310 for the next TTI.

In FIG. 8C, stage 320 represents preferred procedures for the steadystate portion of downlink outer loop power control. In step 321, the TTIcount for the observation period is initialized to zero. At step 322,the number of CRC errors N_(E) is checked as to whether at least oneerror was detected in the current TTI. If at least one error isdetected, then steady state parameters step down SD_(S) and step upSU_(S) are adjusted according to Equations 3 and 4 (step 325). Thetarget SIR step size is set to the steady state step size SS_(SS)determined in step 302. The target SIR value is adjusted according tothe following equation:target_SIR=current_target_(—) SIR+SU _(S) −SD _(S)(N _(B) −N _(E) /N_(E))  Equation 9where N_(B) is the number of transport blocks received on the referenceTrCH in the current TTI, and N_(E) is the number of transport blocksreceived with a CRC error on the RTrCH in the current TTI. The purposeof scaling the step down by (N_(B)−N_(E))/N_(E) is to minimize theabsolute variation in target SIR. An alternative approach would be toincrease target SIR by step up SU_(S) for each block in error (i.e., bySU_(S)*N_(E)) while decreasing by step down SD_(S) for each blockreceived without error (i.e., by SD_(S)*(N_(B)−N_(E)). However, thisalternative approach results in greater overall variations in the targetSIR upon detection of a CRC error, since step up SU_(S) isproportionately large compared to SD_(S).

Also at step 325, the current value of detected CRC errors N_(E) isstored as follows: Last_N_(E)=N_(E). The stored error value Last_N_(E)is useful for future TTI processing in which no CRC errors are detected,and a division-by-zero operation is averted in step 326. At step 325,the new target SIR value is checked for being no greater than valueMaximum_DL_SIR. If the new target SIR is found to be greater than thismaximum value, the new target SIR is reset to value Maximum_DL_SIR. Thesteady state continues by returning to step 322.

Returning to step 322, if there are no detected errors N_(E), then theobservation period is checked (step 323) for being greater than or equalto a threshold, preferably a threshold equal to 5/(target BLER). Whenthe observation period reaches a value greater than this threshold, step324 commences where the step down value SD_(S) is doubled. However, theobservation period will initially be less than the threshold, in whichcase step 324 is skipped, and the target SIR is decreased (step 326) asfollows:target_SIR=current target_SIR−SD _(S)(N _(b)/Last_(—) N _(E))  Equation10If this new target SIR value is less than a minimum valueMinimum_DL_SIR, the new target SIR is set to the minimum valueMinimum_DL_SIR. Otherwise, it remains at the calculated value. Next, theobservation period is incremented by one and the algorithm returns tostep 322. The algorithm 320 then repeats until the CCTrCH becomesinactive.

Preferably, the components that implement the algorithms illustrated inFIGS. 5-8 are implemented on an single integrated circuit, such as anapplication specific integrated circuit (ASIC). However, portions of thealgorithms may also be readily implemented on multiple separateintegrated circuits.

The foregoing description makes references to outer loop power controlin the context of a 3GPP system as an example only and not as alimitation. The invention is applicable to other systems of wirelesscommunication including GSM, 2G, 2.5G or any other type of wirelesscommunication system where the equivalent of outer loop power control isimplemented. Other variations and modifications consistent with theinvention will be recognized by those of ordinary skill in the art.

1. A method of downlink outer loop transmission power control having asettling state, a transient state and a steady state, comprising: duringthe settling state: initializing a steady state step size parameter anda transient state step size parameter, and converging a measured signalto interference ratio (SIR) to an initial target signal to interference(SIR) using an inner loop power control; during the transient state: foreach transmission time interval (TTI), setting a transient state stepdown parameter based on a target block error rate parameter and atransient state step size parameter, and setting a transient state stepup parameter based on the transient state step down parameter and atransient state step size parameter, where the transient state step downparameter and the transient state step up parameter are used foradjusting the target SIR; adjusting the transient state step sizeparameter by half upon detection of an error during a TTI; andincreasing the target SIR if an error is detected and decreasing thetarget SIR if no error is detected and the transient state step size isgreater than the steady state step size; during the steady state: foreach TTI, decreasing the target SIR by a steady state step downparameter if no error is detected and increasing the target SIR if anerror is detected; and increasing the steady state step down parameterif no error is detected within an observation period of multiple TTIs.2. The method of claim 1, wherein the initial transient state step sizeparameter (SS_TS) is calculated relative to the target BLER as follows:SS_TS=2log10(1/target_BLER).
 3. The method of claim 1, wherein theinitial steady state step size parameter (SS_SS) is calculated relativeto the target BLER as follows: SS_SS=0.25[log10 (1/target_BLER)].
 4. Themethod of claim 1, wherein the initial steady state step size parameteris equal to ⅛ of the initial transient state step size parameter.
 5. Themethod of claim 1, wherein the steady state step down parameter isfactored by the number of received transport blocks within the TTI (NB)minus the number of transport blocks with a detected error (NE) per NE.6. The method of claim 5, wherein during the steady state, the targetSIR is adjusted as follows upon detection of an error: targetSIR=current target SIR+steady state step size parameter−steady statestep down parameter−the factored steady state step down parameter. 7.The method of claim 1, further comprising leaving the transient stateand entering the steady state once the transient state step size isreduced to an amount equal to or less than the initial steady state stepsize upon receiving enough detected errors.
 8. The method of claim 1,wherein the observation period equals the ratio of 5 divided by thetarget BLER value.